Commonly used fluorescent lamp ballast are of the rapid start type which includes a transformer primary winding and a secondary winding supplying operating current to the lamp, and also one or more heater windings which supply current through the filaments at each end of the fluorescent lamp. The heating current is supplied when power is switched on to the ballast and resistively heats the filaments to emmissive state. In this state a relatively low voltage, and hence a smaller and less expensive ballast, is needed to ignite an arc across the lamp. Heating the filaments protects them from damage which would occur with cold ignition, and prolongs lamp life.
The rapid start ballast circuit has the disadvantage that heater current continues to flow when not needed after the lamp starts, and accordingly it is an object of the invention to eliminate the waste of continuous heater current while retaining the advantages of rapid starting.